Optimization Of Municipal Garbage Mechanical Dewatering Wastewater Treatment

The mechanical dewatering wastewater(MDW)from municipal garbage is a mixture wastewater,which is rapidly sqeezed from fresh municipal garbage by means of high pressure extrusion.The characteristics of this MDW include complex compositions,high concentration of suspended solids(SS),organic matter and ammonia nitrogen,and large change of water content.In this study,an integrated treatment system comporised of physical pretreatment,coagulation and sedimentation treatment,anaerobic sequencing batch reactor(ASBR),sequencing batch reactor(SBR)for short-nitrification and denitrification,and UV/O3 advanced treatment,was developed and optimized from lab-scale to pilot scale,which could stably treat MDW with high cost-effectiveness.The lab-scale ASBR was start-up after 55 d operation,whose COD removal rate could reach over 95.2%.The SBR for short-nitrification was operated by using on-line p H control combined with DO control,to achieve a stable inhibition of nitrite oxidation bacteria(NOB),and to achieve continuous nitrite accumulation,and then the ammonia removal rate of 95.4% and the NAR of 83% were obtained.The short-cut denitrification was carried out in a SBR and was start-up in a month,whose denitrification efficiency stable reached to 99.0%.With an influent TN concentration of 800 ± 50 mg / L,the effluent TN maintained below 40 mg/L.By using UV/O3 advanced treatment with a hydraulic retention time(HRT)of 120 min,the COD removal rate could maintained at about 74.5%.After a long-term system operation,the optimized operation condition parameters of the integrated system were obtained to guide real practical application.The pre-treatment process was addition of Na HCO3 to adjust p H to over 9,and the coagulation and sedimentation process included the dosage of PAC and PAM of around 850 and 2 mg/L,respectively,with a stirring mode of 250 r/min rapid mixing followed by 1 min 50 r/min slow mixing.As for the ASBR process,an intermittent stirring mode of on /off of 10 min/60 min was applied to remove COD.The short-cut nitrification SBR was operated with a DO below 1.0 mg/L,a p H ranged from 7.5 to 8.0,and an HRT of 24 h to stable maintain nitrite accumulation.Meanwhile,the SBR for short-cut denitrification was achieved with a C/N of 3.5 and an HRT of 24 h.Finally,the UV/O3 system was operated with the condition of ozone dosage of 20 mg/min and an HRT of 120 min to remove COD.The pilot-scale integrated system results showed that the overall COD removal rate was above 99.6% with an effluent COD was as low as 100 mg/L,and short-cut nitrification and denitrification could remove more than 96.4% ammonium nitrogen,96.1% of total nitrogen with a NAR of 80%.Therefore,the effluent can stably satisfy the discharge standard in the “landfill pollution control standards”(GB 16889-2008).This integrated system possessed the advantages of low energy consumption,short treatment chain,and stbale efflutent quality.For a treatment capacity of 500 m3/d,the system economy analyzed results demonstrated that the investment for system infrastructure and equipment was 2.09 million,and the system operate costs was 4.99 million per year,and the annual recovery of electricity value was about 81 thousand.